1. Field of the Invention
The present invention relates to an overvoltage protection circuit and an electronic device comprising the overvoltage protection circuit. More particularly, the present invention relates to an overvoltage protection circuit capable of preventing an overvoltage from being applied from a power source to a circuit included in an electronic device or the like, and relates to an electronic device including the overvoltage protection circuit.
2. Description of the Background Art
Conventionally, there have been overvoltage protection circuits for preventing voltage from being oversupplied to a circuit from a power source such as an AC adaptor or the like. For example, Japanese Laid-Open Patent Publication No. 2004-229365 (hereinafter, referred to as Patent Document 1) discloses an overvoltage protection circuit (a voltage-limiting circuit) for protecting a circuit from overvoltage. The overvoltage protection circuit has a voltage limiter for limiting voltage at both ends thereof to a predetermined voltage value. By connecting a circuit to be protected (to-be-protected circuit) and the voltage limiter in parallel, the overvoltage protection circuit prevents a voltage, which is no lower than the voltage at both the ends of the voltage limiter, from being applied to the to-be-protected circuit.
Since the voltage limiter in the overvoltage protection circuit disclosed in Patent Document 1 is structured with such an element as a diode or the like, it is difficult to precisely set a limit voltage value. In order to improve the precision in setting the limit voltage value for the above overvoltage protection circuit, it is conceivable to incorporate, into the overvoltage protection circuit, a voltage detection integrated circuit for detecting a value of a voltage supplied to the to-be-protected circuit. To be specific, the value of the voltage supplied to the to-be-protected circuit is detected by the voltage detection integrated circuit, and in accordance with a result of the detection, whether to limit (or cease) or allow the supply of the voltage is controlled. However, the voltage detection integrated circuit is not capable of enduring overvoltage. For this reason, if the voltage detection integrated circuit is simply incorporated into the over voltage protection circuit, the voltage detection integrated circuit is destroyed due to an overvoltage supplied thereto, which finally leads to failure to securely prevent an overvoltage from being supplied to the to-be-protected circuit.